The present invention relates to a machine for making filter bags for products for infusion, such as tea, coffee, chamomile, etc.
In the present description, the filter bags of particular interest are of the single-lobe type (that is to say, with a single chamber which contains the product for infusion), with heat-sealing on three edges of the filter bag and folding of the fourth, with the addition of a thread and pick-up tab for the infusion process which is connected to the filter bag.
Known machines for making this type of product normally have: a reel which feeds a continuous web of heat-sealable material to a station at which the web is folded over itself to create a pocket which receives individual doses of the product for infusion arriving from a product dosing station; a station which seals three edges of the filter bag and heat-seals the thread with pick-up tab to the filter bag, the tab having been attached to one end of the thread at an attachment station; the thread and tab are prepared in a station located substantially at the side of the sealing station. There is also a station which cuts the individual filter bags and the thread with tab; a station for winding the thread with tab around the filter bag and simultaneously transferring the individual filter bags with wound thread and tab to an attachment station, which attaches the tab to one sealed edge, more specifically the end, of the filter bag.
Downstream of the latter station there may also be a station for preparation of outer wrappers for the filter bag; a station which stacks a preset number of filter bags with or without outer wrappers; and, finally, a station which packs groups of filter bags into boxes.
At present, machines of the type described above are limited from the point of view of operating speed in the production of filter bags in a given time.
These limitations are caused by the structure of some stations, in particular, the station which attaches the tab to the thread, the station which winds the thread with tab around the filter bag and the station which attaches the tab to the sealed end of the filter bag.
Both the station which attaches the tab to the thread and the station which attaches the label to the sealed end of the filter bag comprise gluing units for the application of an adhesive on an area of the tab and on an area of the sealed side of the filter bag, these gluing units making the attachment operations relatively slow and sometimes leaving adhesive waste or impurities on the product.
The station which winds the thread around the filter bags consists of a wheel which turns about its own horizontal axis, with a plurality of grippers evenly distributed along the circumference of the wheel and each designed to pick up an individual filter bag, whilst the thread and tab remain free close to the bag, that is to say, in contact with the outer surface of the wheel opposite that on which the grippers are fitted. As the wheel turns, this free pre-winding configuration tends to create a pendulum action by the thread and tab (with free, random positioning), which may cause the thread to go beyond the wheel or to a position which is not suitable for correct complete thread winding around the filter bag.
This pendulum action is accentuated as the machine speed increases, with a consequent increase in the speed at which the wheel turns. As a result, in order to keep the position of the thread with tab as correct as possible on the wheel, given that for winding transfer the thread must be centered relative to the filter bag, the machine production speed must be kept low.
The aim of the present invention is, therefore, to overcome the above-mentioned disadvantages by providing a machine designed for making filter bags for products for infusion whose production speed is decidedly higher than that of conventional machines, without completely changing the basic structure of the conventional machine.
Accordingly, a machine is provided for making filter bags for products for infusion comprising, close to a first wheel, which forms a station for winding a thread with pick-up tab around a filter bag, means which position and guide the thread with pick-up tab relative to the corresponding filter bag. The positioning means operate along an arced path covered by the filter bag in order to wind the thread with pick-up tab around it and said means can keep the thread with pick-up tab in a substantially stable and well-defined position relative to the filter bag along the arced winding path.